Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$143.73	5.501%	$151.6366	$151.64	$151.65	$151.60
Purchase #2	$85.75	13.396%	$97.2371	$97.24	$97.25	$97.20
Purchase #3	$39.35	10.251%	$43.3838	$43.38	$43.40	$43.40
Purchase #4	$105.45	11.446%	$117.5198	$117.52	$117.50	$117.50
Purchase #5	$140.84	4.182%	$146.7299	$146.73	$146.75	$146.70
Purchase #6	$36.40	3.141%	$37.5433	$37.54	$37.55	$37.50
Purchase #7	$33.61	6.836%	$35.9076	$35.91	$35.90	$35.90
7 purchase totals =	$585.13		$629.9581	$629.96	$630.00	$629.80